This study proposes to investigate hearing aid acoustics. The study will have four phases of investigation. The first phase will be a study of the acoustic filter effect of the earmold on the output of the hearing aid. The second phase will study the relationship between the acoustic impedance of the hearing aid receiver and ther earmold. The third phase will investigate the effect of the earmold vent on sound incident upon the earmold. The fourth phase will study the relationship of head diffraction effects and hearing aid microphone placement. The results of this study should allow specification of optimal coupling of hearing aid receivers to earmolds and should allow specification of optimal location of the hearing aid microphone.